Methods to produce roof tiles using cement, sand and water, are well known. U.S. Pat. No. 4,673,659 teaches a method of mixing cement, sand and water, extruding the mix by the well-known roller and slipper method, cutting the extruded mix to provide sections of the required length and curing at elevated temperatures under conditions of high humidity. Roof tiles of essentially flat or convoluted constructions are made in this way. Typically, they have densities ranging from 2.1-2.2 g/cc. Typical U.S. interlocking roof tiles have dimensions of about 422 mm (length).times.333 mm (width).times.11.5 to 12.5 mm (thickness). Such tiles usually weigh 4.2 to 5.0 kg/tile, with strengthening ribs, nibs and weatherchecks, which are provided on the undersides of the concrete interlocking roof tiles. Conventional concrete roof tiles of the kind described above provide a satisfactory and highly durable roofing material and are extensively used for the roofing of new houses and other buildings with sufficient supports. However, conventional concrete roof tiles are heavy and cannot replace lighter weight roofing materials such as wood shingles and shakes, asphalt shingles, slates, etc., because the building structure cannot support the additional load. For example, with timber framed buildings, it is often necessary to reinforce the existing roof timbers to ensure that they will bear the additional load. This is costly and time consuming, and often leads to abandoning the use of concrete roof tiles for re-roofing work.
Thus, there is continuous need for concrete roof tiles which are lighter in weight than conventional concrete roof tiles but have the adequate strength and durability of conventional concrete roof tiles. Such strong, durable lightweight concrete roof tiles will be useful as a suitable replacement for wood shingles and shakes, asphalt shingles, asbestos cement roofings, slates, etc.
U.S. Pat. No. 5,395,442 to Dunton, et al., (hereinafter referred to as "Dunton, et al.") discloses lightweight concrete roof tiles using latex. Dunton, et al.'s composition consists essentially of: 45-65 parts by weight of an acrylic latex emulsion; 130-180 parts by weight of a cement; 360-400 parts by weight of a lightweight aggregate; and 50-75 parts by weight of additional water.